Germany: In most cases, patients who experienced an adverse inflammatory skin reaction after receiving subcutaneous heparin tolerated administration of the drug via IV, says an article published in The Journal of Allergy and Clinical Immunology: In Practice.
The most common heparin allergy symptom is delayed-type hypersensitivity (DTH), which results in an itchy, inflammatory skin reaction where the drug was injected subcutaneously. Heparin-induced thrombocytopenia-related circumscribed cutaneous necrosis is an essential differential diagnosis. Axel Trautmann and team expressed concerns that may develop, in particular in an emergency case necessitating intravenous heparin administration if a patient experiences an inflammatory skin reaction to subcutaneously administered heparin.

For this study, over the course of the last 17 years, all cases of heparin DTH observed in the department underwent challenging testing, which involved intravenous administration of unfractionated heparin and subcutaneous injection of fondaparinux (UFH).
The key findings of this study were as follows:
1. DTH was discovered in 48 (96.0%) of the 50 patients with proven heparin allergy, while only two other patients were identified with immediate-type, most likely IgE-mediated hypersensitivity (4.0%).
2. Intradermal testing on the 48 DTH patients demonstrated significant cross-reactivity between UFH and LMWH, such as nadroparin, dalteparin, and enoxaparin.
3. Only three (6.3%) occurrences of cross-reactivity with (or concurrent sensitization to) fondaparinux were observed.
4. Despite DTH to UFH and LMWH, as shown by intradermal testing, intravenous injection of UFH was tolerated by all 45 individuals tested.
In conclusion, according to the researchers, how heparin is delivered may affect how well it is tolerated. Heparin, however, mostly stays in the bloodstream after IV treatment, attaches to plasma proteins, and degrades quickly. Heparin may then be administered intravenously to patients with suspected or confirmed DTH who are having open heart surgery, hemodialysis, or other life-threatening circumstances.
heparin-relatedThe tissue around the site of the subcutaneous injection contains relatively high amounts of heparin, which causes a T-cell-mediated heparin-related immunological reaction. The best substitute for subcutaneous administration is fondaparinux.
Reference:
Trautmann, A., Grän, F., & Stoevesandt, J. (2022). Delayed-Type Heparin Allergy: Intravenous Tolerance Despite Inflammatory Skin Reaction After Subcutaneous Injection. In The Journal of Allergy and Clinical Immunology: In Practice. Elsevier BV. https://doi.org/10.1016/j.jaip.2022.06.030